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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef js_Fifo_h
#define js_Fifo_h
#include <algorithm>
#include <utility>
#include "js/Vector.h"
namespace js {
// A first-in-first-out queue container type. Fifo calls constructors and
// destructors of all elements added so non-PODs may be used safely. |Fifo|
// stores the first |MinInlineCapacity| elements in-place before resorting to
// dynamic allocation.
//
// T requirements:
// - Either movable or copyable.
// MinInlineCapacity requirements:
// - Must be even.
// AllocPolicy:
// - see "Allocation policies" in AllocPolicy.h
template <typename T, size_t MinInlineCapacity = 0,
class AllocPolicy = TempAllocPolicy>
class Fifo {
static_assert(MinInlineCapacity % 2 == 0, "MinInlineCapacity must be even!");
protected:
// An element A is "younger" than an element B if B was inserted into the
// |Fifo| before A was.
//
// Invariant 1: Every element within |front_| is older than every element
// within |rear_|.
// Invariant 2: Entries within |front_| are sorted from younger to older.
// Invariant 3: Entries within |rear_| are sorted from older to younger.
// Invariant 4: If the |Fifo| is not empty, then |front_| is not empty.
Vector<T, MinInlineCapacity / 2, AllocPolicy> front_;
Vector<T, MinInlineCapacity / 2, AllocPolicy> rear_;
private:
// Maintain invariants after adding or removing entries.
void fixup() {
if (front_.empty() && !rear_.empty()) {
front_.swap(rear_);
std::reverse(front_.begin(), front_.end());
}
}
public:
explicit Fifo(AllocPolicy alloc = AllocPolicy())
: front_(alloc), rear_(alloc) {}
Fifo(Fifo&& rhs)
: front_(std::move(rhs.front_)), rear_(std::move(rhs.rear_)) {}
Fifo& operator=(Fifo&& rhs) {
MOZ_ASSERT(&rhs != this, "self-move disallowed");
this->~Fifo();
new (this) Fifo(std::move(rhs));
return *this;
}
Fifo(const Fifo&) = delete;
Fifo& operator=(const Fifo&) = delete;
size_t length() const {
MOZ_ASSERT_IF(rear_.length() > 0, front_.length() > 0); // Invariant 4.
return front_.length() + rear_.length();
}
bool empty() const {
MOZ_ASSERT_IF(rear_.length() > 0, front_.length() > 0); // Invariant 4.
return front_.empty();
}
// Iterator from oldest to yongest element.
struct ConstIterator {
const Fifo& self_;
size_t idx_;
ConstIterator(const Fifo& self, size_t idx) : self_(self), idx_(idx) {}
ConstIterator& operator++() {
++idx_;
return *this;
}
const T& operator*() const {
// Iterate front in reverse, then rear.
size_t split = self_.front_.length();
return (idx_ < split) ? self_.front_[(split - 1) - idx_]
: self_.rear_[idx_ - split];
}
bool operator!=(const ConstIterator& other) const {
return (&self_ != &other.self_) || (idx_ != other.idx_);
}
};
ConstIterator begin() const { return ConstIterator(*this, 0); }
ConstIterator end() const { return ConstIterator(*this, length()); }
// Push an element to the back of the queue. This method can take either a
// |const T&| or a |T&&|.
template <typename U>
[[nodiscard]] bool pushBack(U&& u) {
if (!rear_.append(std::forward<U>(u))) {
return false;
}
fixup();
return true;
}
// Construct a T in-place at the back of the queue.
template <typename... Args>
[[nodiscard]] bool emplaceBack(Args&&... args) {
if (!rear_.emplaceBack(std::forward<Args>(args)...)) {
return false;
}
fixup();
return true;
}
// Access the element at the front of the queue.
T& front() {
MOZ_ASSERT(!empty());
return front_.back();
}
const T& front() const {
MOZ_ASSERT(!empty());
return front_.back();
}
// Remove the front element from the queue.
void popFront() {
MOZ_ASSERT(!empty());
front_.popBack();
fixup();
}
// Convenience utility.
T popCopyFront() {
T ret = front();
popFront();
return ret;
}
// Clear all elements from the queue.
void clear() {
front_.clear();
rear_.clear();
}
// Clear all elements for which the given predicate returns 'true'. Return
// the number of elements removed.
template <class Pred>
size_t eraseIf(Pred pred) {
size_t frontLength = front_.length();
front_.eraseIf(pred);
size_t erased = frontLength - front_.length();
size_t rearLength = rear_.length();
rear_.eraseIf(pred);
erased += rearLength - rear_.length();
fixup();
return erased;
}
size_t sizeOfExcludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
return front_.sizeOfExcludingThis(mallocSizeOf) +
rear_.sizeOfExcludingThis(mallocSizeOf);
}
size_t sizeOfIncludingThis(mozilla::MallocSizeOf mallocSizeOf) const {
return mallocSizeOf(this) + sizeOfExcludingThis(mallocSizeOf);
}
};
} // namespace js
#endif /* js_Fifo_h */
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